﻿<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title>验证是否为空</title>
		<style>
			body{
				background: #ddd;
			}
			.tips{
				width: 430px;
				height: 40px;
				margin: 5px auto;
				background: #fff;
				color: red;
				border: 1px solid #ccc;
				line-height: 30px;
				padding-left: 30px;
				font-size: 14px;
				display: none;
			}
			.box{
				background: #fff;
				padding: 20px 30px;
				width: 400px;
				margin: 0 auto;
				text-align: center;
			}
			.ipt{
				width: 260px;
				padding: 4px 2px;
			}
			span{
				width: 70px;
				display: inline-block;
				text-align: right;
			}
			.btn{
				width: 180px;
				height: 40px;
				background: #3388ff;
				border: 1px solid #fff;
				color: #fff;
				font-size: 14px;
			}			
		</style>
	</head>
	<body>
		<div id="tips" class="tips"></div>
		<div class="box">
			<p>
				<span>用户名：</span><input id="user" class="ipt" type="text" />
			</p>
			<p>
				<span>密    码：</span><input id="password" class="ipt" type="password"/>
			</p>
			<p>
				<button id="login" class="btn">登录</button>
			</p>			
		</div>
		<script>
		var user=document.getElementById('user');
		var password=document.getElementById('password');
		var tips=document.getElementById('tips');
		
		user.addEventListener('blur',myfun,false);
		password.addEventListener('blur',myfun,false);
		
		function myfun(){
			//判断文本是否为空，若为空则将tips显示，tips内容；若不为空tips隐藏
			//事件对象event， event.target 触发事件的对象元素
			//获取触发事件的元素：user\password
			var obj=event.target;
			if(obj.value==''){
				tips.style.display='block';
				tips.innerHTML="内容不能为空";
			}else{
				tips.style.display='none';
			}
			}
		</script>
	</body>
</html>
